1. Field of the Invention
The present invention relates generally to a testing apparatus for a power transmission of an automotive vehicle, which performs testing performance of the power transmission. More specifically, the invention relates to a transmission testing apparatus which employs an electric motor as a driving power source providing equivalent power characteristics for permitting testing of transition characteristics of the transmission.
2. Description of the Background Art
In the prior art, most transmission testing apparatus employ an automotive internal combustion engine, for which a power transmission to be tested is to be coupled, as a driving power source. The transmission test apparatus performs endurance tests and gear shifting transition tests and so forth. Such conventional testing apparatus have had various problems.
For instance, in order to use the internal combustion engine, various engine accessories, such as a fuel supply system, exhaust system, ignition system and so forth, are required. Furthermore, in order to maintain the clean testing environment, a ventilation system, a noise-proof facility and so forth are required. In addition, since the fuel used for driving the engine has high flashing ability, high attention has to be paid to flashing. Because of various requirements for the facility, cost and administration becomes substantially high. Furthermore, setting up the facility requires substantial working times and causes degradation of testing efficiency.
Second, the internal combustion engine tends to be influenced by environmental conditions, such as atmospheric temperature, atmospheric pressure and so forth, and this varies engine output. Therefore, the result of a test can be fluctuated by the engine condition and environmental condition. Therefore, reliability of the test result is held at a low level.
Also, since the test is performed by utilizing the engine to be actually used with the transmission, the transmission test cannot be performed unless the actually used engine is provided. Namely, when a new engine and transmission are to be developed, testing of the transmission cannot be performed until the engine designing is completed. Therefore, development of the transmission is always delayed in relation to timing of completion of the engine design.
In order to solve the foregoing problems, Japanese Patent First (unexamined) Publications (Tokkai) Showa 58-38833 and 61-53541 propose motor powered transmission testing apparatus which employs an electric motor, a hydrostatic motor as driving power source. Such prior proposed motor powered transmission testing apparatus is effective for performing endurance test and steady state characteristics test. However, because of much greater inertia moment in the motor, a difficulty is encountered in shifting transition characteristics test which is importance for analysis of shifting shock and enhancing transmission shifting characteristics.
Namely, in case of the electric motor, the inertia moment becomes in excess of ten times of that of the internal combustion engine, as set out in Tokkai Showa 61-53541 set forth above. For avoiding influence of the substantially large inertia moment of the electric motor, a command value of a current command for the electric motor is corrected for compensating difference of inertia moment and adapting transition characteristics of driving torque when the set torque varies.
In this case, though the driving torque transition characteristics can be adjusted to be equivalent to that of the actual engine, the revolution speed of the motor fluctuates due to variation of the current command value to make it difficult to obtain transmission shifting transition characteristics data equivalent to that obtained utilizing the actual engine.
On the other hand, the hydrostatic motor which is normally used in combination with a speed increasing device, generally increases the motor revolution speed twice or three times. By utilizing the speed increasing device, the inertia moment in the driving power source can be reduced. However, the prior proposed hydrostatic motor powered transmission test apparatus is still unsatisfactory in avoiding influence of the inertia moment.
As will be appreciated from the discussion given hereinabove, the following power output characteristics may be required for a power source unit to be used as replacement of the internal combustion engine.
First of all, the inertia moment in revolution may have substantial influence for mode of shift shock to be caused in the power transmission. Therefore, the inertia moment on the motor has to be significantly reduced.
Secondly, because the motor has substantial mechanical delay in responding to variation of the electric command, response characteristics equivalent to that of the engine in relation to the throttle valve angular displacement. Particularly, upon starting of vehicular traveling, the throttle angular displacement becomes substantial. In general, the motor cannot follow such abrupt variation of the commanding value. Therefore, the response characteristics of the motor upon vehicular starting-up becomes far different from that of the engine. Therefore, unless the power output characteristics is adapted to be equivalent to that of the engine, shifting transition characteristics of the transmission cannot be obtained as a reliable data.